Apparatus and method for conversion of animal litter biomass into useful energy

Abstract

A method of converting animal litter biomass into useful energy includes the steps of both combusting and pyrolising the biomass, of mixing the resultant combustible gas from the pyrolysis step with the gases from the combustion step, of igniting the mixture of gases ad and feeding the hot mixture of gases to a thermal recuperator; and apparatus therefor.

We claim: 
     
         1 . A method of converting animal litter biomass into useful energy, said method comprising the steps of:
 feeding said biomass in comminuted form into a primary combustion zone comprising an upper region and a lower region;   partially combusting the biomass at the lower region of the primary combustion zone at an elevated temperature in the presence of a combustion-sustaining medium thereby to provide heat into the upper region thereof for pyrolysis to generate combustible gases;   subjecting partially combusted incandescent biomass in the lower region to air flow to generate combustion gases;   mixing the combustion gases and the combustible gases in a mixing chamber;   igniting the resultant mixture of gases thereof to produce a hot gaseous product; and   passing the hot gaseous product to a thermal recuperator for expending and exploiting the heat energy thus produced.   
     
     
         2 . The method of  claim 1 , wherein the incandescent biomass is combusted in a further combustion zone surrounding the zone and the combustion gases therefrom are mixed with the combustible gases from the pyrolysis of the biomass. 
     
     
         3 . The method of  claim 1 , wherein the hot gaseous product passes to a heat exchange zone wherein it is caused to undergo heat exchange with the mixture of gases from the mixing chamber. 
     
     
         4 . The method of  claim 3 , wherein turbulence is imparted to the flow of gases within the heat exchange zone by the provision of baffles thereby to lengthen the residence time of gases within the zone and to enhance both the suppression of noxious elements within the gases and the heat transfer efficiency. 
     
     
         5 . An apparatus for the conversion of animal litter biomass into useful energy, the apparatus comprising:
 a primary combustion zone incorporating a chamber of frusto-conical form;   a feed entry to the primary combustion zone;   a feed conduit contiguous with said primary combustion zone and connected to the feed entry at a relatively upper region of the primary combustion zone;   a combustible gas outlet for the primary pyrolysis combustion zone formed in the upper region;   a rotatable grate situated at the lower region of the primary combustion zone;   a means for rotating the grate;   a combustion-sustaining fluid distributor located at the lower region;   a secondary normal combustion zone on the grate circumscribing the lower region of the primary pyrolysis combustion zone;   a combustion exhaust gas outlet from the secondary combustion zone;   a gas mixing zone downstream of the combustible gas outlet and the combustion exhaust gas outlet wherein in use the respective combustion gases and the combustible gas mix;   an ignition station for the resultant mixture of gases, the gas mixing zone comprising at least a partial tube bank for reheating and suppression of pollutant emissions; and   a final gas discharge flue for the resultant gases.   
     
     
         6 . The apparatus of  claim 5 , wherein gas mixing zone includes a heat exchange zone for expending and exploiting the heat energy of the hot mixture thus produced. 
     
     
         7 . The apparatus of  claim 5 , wherein the apparatus is of generally cylindrical form. 
     
     
         8 . The apparatus of  claim 5 , wherein comminuting means is provided for comminuting the biomass feedstock. 
     
     
         9 . The apparatus of  claim 8 , wherein the comminuting means comprises a hopper with a rotatable armature provided with blades. 
     
     
         10 . The apparatus of  claim 9 , wherein a rotatable disc is disposed beneath outlet of the hopper for feeding the comminuted feedstock into the feed conduit. 
     
     
         11 . The apparatus of  claim 5 , wherein the combustion-sustaining fluid medium distributor is of foraminous conical form incorporating a plenum chamber with a medium feed conduit connected thereto. 
     
     
         12 . The apparatus of  claim 6 , wherein the gas mixing zone comprises a full tube bank of coiled tubes. 
     
     
         13 . The apparatus of  claim 6 , wherein the gas mixing zone comprises a demi-tube bank of coiled tubes. 
     
     
         14 . The apparatus of  claim 6 , wherein baffles are provided in the heat exchange zone. 
     
     
         15 . The apparatus of  claim 5 , wherein a solid waste collection area is defined beneath the rotatable grate, and a discharge outlet is provided therefor and leads to a removal station. 
     
     
         16 . The apparatus of  claim 5 , wherein the secondary normal combustion zone is defined externally of the primary combustion zone, the secondary zone being provided with air distributor tubes.